This invention relates to electrostatographic reproducing apparatus and more particularly to a two cycle automatically operated compact copier structure. The electrostatic reproduction art has grown from the very early commercial models which included the early multi unit flat plate equipment available from Xerox Corporation which used separate charging, exposure, developing and fusing units to the Xerox 9200 family of products which is fully automated high speed complicated reproducing apparatus with sophisticated exposure document handling as well as copy sheet handling apparatus. Most of the commercial reproducing apparatus commonly in use today use a photoconductive insulating member which is typically charged to a uniform potential, thereafter exposed to a light image of an original to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to image areas contained within the original document. Subsequent to the formation of the electrostatic latent image on the photoconductive insulating surface, it is made visible with a developing powder referred to in the art as toner. During development the toner particles are attracted to the image areas on the photoconductive insulating area to form a powder image thereon. This image is subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or the application of pressure. Historically, the transfer of toner images to supporting surface such as copy paper is accomplished with electrostatic transfer by either a corotron transfer device or roller electrode biased to transfer potential levels. In corona induced transfer the final support sheet is placed in direct contact with the toner image while the image is supported on the photoconductive surface and the back of the sheet, that is the side of the sheet away from the image is sprayed with a corona discharge having a polarity opposite to that of the toner particles causing the toner to be electrostatically transferred from the photoconductor to the sheet. This system is to a large extent humidity sensitive in that the copy paper which does contain some moisture is sprayed with ions. The moisture in the copy paper makes the paper conductive and charge migrates through the paper thereby distorting the toner image on the paper. This difficulty is compounded by high relative humidity atmospheres since the moisture level of the copy paper is increased.
In bias roll transfer, it is argued that better control of the forces acting on the toner during transfer is had. This type of transfer involves the use of a metal roll with a resistive resilient coating such as that illustrated in U.S. Pat. No. 2,807,233. Because of the resistitivy of the coating, the amount of bias that can be applied to the roll is limited to relatively low operating values, since at the higher range the air in and about the transfer zone begins to breakdown, i.e., ionizes causing the image to be degraded during transfer. In addition, in the pre-transfer or pre-nip region before the copy paper contacts the image if the transfer fields are high the image is susceptible to premature transfer across the air gap leading to decreased resolution or fuzzy images. Further, if there is ionization such as mentioned above with regard to the bias roll transfer in the pre-nip air gap from high fields, it may lead to strobing or other image defects, loss of transfer efficiency and a lower latitude of system operating parameters. Yet in the directly adjacent nip region itself, the transfer field should be as large as possible to achieve high transfer efficiency and stable transfer. In the next adjacent post-nip region at the photoconductor copy sheet separation or stripping area, if the transfer fields are too low, hollow characters may be generated. On the other hand, improper ionization in the post-nip region may cause image instability or copy sheet detacking problems. Variations in conditions of copy paper contaminents, etc., can all effect the necessary transfer of parameters. Furthermore, the bias roll material resistivity and paper resistivity can change greatly with humidity. In order to minimize these difficulties various materials have been used in bias roll transfer systems which because of the degree of sophistication of fabricating them are extremely expensive. Following the transfer of the toner image to the support surface the photoconductive insulating layer is cleaned of residual toner to prepare it for the next imaging cycle.
While there has been ever increasing desire for an increased degree of sophistication and capability with regard to such automatic reproducing equipment there continues to remain a need in the low volume, slower, smaller apparatus part of the marketplace. This is particularly necessary to supply small businesses and individuals with a capability to reproduce original documents in a slower manner and at reduced costs. This particular segment of the reprographics market is particularly price sensitive. To satisfy this market, there is a continual need to reduce the selling and manufacturing costs. As a corollary, there is a continual desire by the manufactures within this area of the market to provide a smaller box with fewer parts in the total reproducing apparatus. In addition, there is continuing drive in this area of the market to provide portable, lightweight, compact, highly reliable, low cost machines.
Furthermore, even the simplest devices available on the market which automatically feed the documents and copy papers require complicated feed mechanisms including sophisticated clutches and logic assemblies, cam banks, timers, and other mechanical components, all of which require at least initial if not continual adjustment in order to operate satisfactorily. This dramatically increases the cost from the standpoint of both parts costs as well as assembly costs and initial set up and adjustment.